1. Field of the Invention
This invention relates to the field of pumps and, more particularly, to low speed two-stage motor driven pumps.
2. Description of the Prior Art
There are many uses for a pump capable of delivering either a small volume of fluid at a relatively high pressure or a large volume of fluid at a relatively low pressure. Known two-stage fluid pumps are capable of producing the desired outputs. One such known two-stage pump is shown in U.S. Pat. No. 3,614,267 to Schultze wherein a gerotor pump and a radial piston pump are driven by a shaft that telescopes over the motor output shaft. The radial pistons of the radial piston pump are driven successively by a sidewardly facing cam on the output shaft. The uneven radial forces created by the radial pistons have a tendency to cause deflection of the shaft and wear in the bearings supporting the shaft of the motor. The deflection of the shaft also causes the shaft seals to leak with the attendant problems.
U.S. Pat. No. 3,053,186 to Gondek is also directed to two-stage pumps with a gear pump driven directly by the motor shaft and with a wobble plate pump being driven by a shaft connected to the driven gear of said gear pump. The Gondek pump is expensive to build and to maintain, requiring two shafts and mountings therefor. Since Gondek requires two shafts and associated bearings, the resulting pump is bulky and awkward to use.